Automatic regulation of echo-suppressor sensitivity



May 4 1926. 1,582,984

H. S. HAMILTON AUTOMATIC REGULATION OF ECHO SUPPRESSOR SENSITIVITY Filed Sept. 10. 1925 INVENTOR Pilot W e ATTORNEY.

SHamdlton/ 7 echo suppressor.

Patented May 4, 1 926.

UNITED STATES PATENT OFFICE.

HAROLD s. HAMILTON, OF NEW YORK, N. 'Y., AssreNOR To AMERICAN TELEPHONE AND TELEG APH coMrA Y, A CORPORATION OF NEW Y RK.

Application filed September 10, 1925. I Serial No. 55,541.

To all whom, it may concern:

Be it'known that I, HAROLD S. HAMILTON, a citizen of the United States, residing at New York, in the county of Bronx and State of New York, have invented certain Improvements in Automatic Regulation of Echo-Suppressor Sensitivity, of which the following is a specification.

This invention relates to transmission controlling arrangements and'more particularly to arrangements for controlling the sensitivity of echo suppressors used in connection with transmission circuits.

In the operation of long toll circuits, the transmission varies from time to time due to changes in temperature and other causes. It is therefore customary to provide at some repeater point an automatic arrangement which adjusts the gain of the repeater at that point to bring the over-all transmission equivalent back to normal in case the transmission equivalent ofthe circuit has been varied. It is also necessary in some instances, particularly where a cable is employed for the toll circuit, to provide the circuits with echo suppressors which function when talking in one direction to disable the circuit for transmission in the oppositedirection.

It is sometimes necessary to locate the echo suppressor equipment atthe repeater point in the circuit where the transmission ad'ustment is made. At such a repeater point the transmission level at the output of the repeater will vary over a considerable range since the ain of this repeater is changed by a su cient amount to compensate for the transmission changes in an entire regulator section which may have several repeaters in it. As the echo suppressor apparatus must ordinarily be applied to the output side of the repeater, difficulties may be encountered in the satisfactory operation of the echo suppressor due to the change in transmission level at the point where it is applied. i

For example, if the gain of the repeater is increased several transmission units to compcnsate for increased transmission loss of the regulator section, satisfactory echo suppressor operation may be interfered with due to the higher level impressed upon the As the transmission level is raised the noise level is correspondingly elevated, and if the echo suppressor, as is often the case, is adjusted for a close marderstood from the following detailed changed; that is, as the gain of the repeater is increased the sensitivity of the echo suppressor will bereduced by a corresponding amount, and vice versa. An' arrangement operating in the manner stated willhave the result of maintaining substantially constant the net transmission level applied'to the echo suppressor.

The invention may now be more fully Ian- 8- scription thereof when read in connection with the accompanying drawing, the figure of which illustrates a preferred embodiment of the invention.

Referring to the drawing, LE and LW designatethe transmission lines, of a fourwire' circuit provided with one-way repeaters AE and AW at one repeater point. In orderto automatically adjust the'transmission level at the repeater point 'illus trated when the over-all transmission of the circuit departs from normal, due to temperature changes or other-causes, a; pilot points of the bridge and this relay controls.

a suitable mechanism M for adjusting a shaft S carrying switch arms 8' and s". The mechanism whereby the shaft is rotated in one direction or the other, dependin upon the direction of current flow throng the galvanometer, is fully described in I S/Patent No. 1,438,219, issued to A. B. Clark, December 12, 1922, and the details of the shaft of said mechanism are therefore not described herein. If the resistance of the pilot circuit chan es due to a change intemperature, the bridge W is unbalanced, thereby causing current to flow through the galvanometer G in accordance with the direction of unbalance. The deflection of the needle of the galvanometer causes the'shaft S to be rotated step by step in a manner fully described in the Clark patent, thereby causing the switch arm 8 to be rotated until the bridge is a ain balanced. This rotation g produces a corresponding movement of the switch arms 8 so that said switch arm is moved to a different one of the controlling contacts over which it is adapted to ride. This results in applying ground to one of the control wires 1, 2, 3, 4, etc.

The amplifier AE is provided with a potentiometer arrangement PE for determining the gain of the amplifier. This potentiometer arrangement is illustrated schematically but, as is well understood in the art, the setting of the potentiometer is determined by the energization of some one of a group of relays connected to the conductors 1, 2, 3, 4, etc. Similarly, the amplifier AW is provided with a otentiometer arrangement PW whose setting is likewise determined by the energization-of one of a group of relays connected to the conductors 1, 2, 3, 4-, etc. Consequently, when the switch arms a" is shifted to a new position, a different setting of the potentiometer arrangements PE and PW results so that the gain of the two amplifiers is changed in proportion to the transmission change indicated by the pilot wire mechanism.

The echo suppressor arrangement associated with the four-wire circuit comprises two sets of echo suppressor units, one associated with the line LE and the other associated with the line LW upon the output sides of the repeaters AE and AW respectively. The echo suppressor unit associated with the line LE comprises an amplifier SAE and a rectifying tube RE on the output side of which is connected a voice control relay VE. The amplifier functions to amplify the voice currents received and impress them upon the rectifier tube. The rectifier tube has its grid potential so adjusted n its normal operation that no current flows in the plate circuit, but when voice currents are superposed on the normal grid potential, rectified currents correspondin tothe' voice currents will flow through 1'. e relay VE. \Vhcn the relay VE is actuntcd in response to voice currents it closes a short circuit connection in response to voice currents a short circuit connection across the out )ut side of the amplifier AW to prevent echo currents being transmitted back over the line 1 W as the result of d rect transmission over the line LE. The short-circuit connection established also short-circuits the input side of the echo suppressor unit associated with the line LW.

The last mentioned echo suppressor unit likewise comprises amplifier SA W, rectifier tube RW', and voice-operated relay VW operating in the same manner as the corresponding elements of the echo suppressor unit first described. When the relay VVV operates in response to voice currents transmitted over the line'LW it short-circuits the output side of the amplifier AE and also short-circuits the input side of the echo sup-' pressor unit associated with the line LE.

Normal adjustments of the sensitivity of the echosuppressor units may be accomplished by connecting the grids of the amplifiers SAE and SA /V to suitable taps on adjusted in order to bring the over-all transmission of the four-wire circuit back to normal the normal sensitivity adjustment of the echo suppressor units may no longer be satisfactory. If the gain of the amplifiers AE and AW be increased the level of thenoise currents will be raised so that the echo suppressors may respond to noise currents. On the other hand, if the gain of the amplifiers be materially decreased the echo suppressor units may fail to respond to Weak voice currents at the originating ends of the four-wire lines.

it is therefore proposed in accordance with the present invention to automatically change the sensitivity of the echo suppressor units as the Wheatstone bridge arrangement adjusts the setting of the potentiometers PE and PW. As shown in the drawing, this result is accomplished by connecting relays l R R R and R to the wires 1', 2, 3 and 4, over which circuits, may be completed by means of the switch arm 8" of the adjusting mechanism. connect wire 20 to different points upon a potentiometer 21 bridged across the bat-- tery which supplies the normal operating potential to the grids of the rectifiers RE and RVV.

When the regulating apparatus operates to increase the gain of the amplifiers AE and AW the particular relay of the group R R etc., which is'operated willv connect the grids of the rectifier tubes to a point on the potentiometer which is more negative than the point to which the grids were connected before. Obviously, it will then require a greater volume of voice currents to produce rectified currents in the output circuit of the tubes RE and RW. If, on the The contacts of these relays changed in one direction or the other a.

compensating change isinade in the sensitivity of the echo suppressor units so that in effect the rectified "oice currents operating the relays VE andVlV will be the same regardless of the adjustment of the amplifiers'AE and AIV for a given "olume of current applied at the transmitting end of the circuit. g

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit andscope of the appended claims. R m

IVhat is'claimed is:

1. In a signaling system, a transmission circuit, a variable-transmission element associated with said circuit, means to automatically var the transmission of said transmission e ement in response to changes 'in the over-all transmission equivalent of said circuit, an echo suppressor associated 'with said circuit, and means automatically responsive to changes in the adjustment of said transmission element to pensating changes in the sensitivity of the echo suppressor.

2. In a signaling system, a' transmission circuit, a variable transmission element associated' with said circuit, mechanism automatically responsive to changw in the overall transmission of said circuit to vary the adjustment of said transmission element, an echo suppressor associated with said'circuit, and means automatically contro led by said automatic mechanism for automatically adjusting the sensitivity of'said echo sup pressor.

3. In a signalingsystem, a transmission j circuit, a variable transmission element associated therewith, automatic mechanism remal v circuit, a variable transmission element assosponsive to changes in the transmission equivalent of said circuit to variably adjust said transmission element, an echo su pressor including a vacuum tube associate with said circuit,-and means controlled by said.

automatic mechanism ,for varying the norpotential applied to the grid 'of said tube. I I '1 g "V 4. In a signaling system, a transmission produce comgain of said amplifiers.

name to this specification ciated with said circuit, a pilot conductor sub-- jected to transmission conditions similar to those affecting said transmission circuit, an

automatic adjusting device responsive to changes in the current flow in said pilot circuit,'means controlled by said automatic adjusting device for automatically adjusting the transmission of said transmission element, an echo suppressor associated, with said transmission circuit, and means controlled by said automatic adjusting device for adjusting thesensitivity of said echo suppressor. v

'5.- In a signaling system, a transmission circuit, a variable transmission element associated with said circuit, a pilot conductor subjected to transmission conditions similar to those affecting said transmission circuit, an automatic adjusting device responsive to changes in the current flow in said pilot circuit, means controlled by said automatic adj usting device for automatically adjusting the transmission of said transmission element, an echo suppressor associated with said transmission circuit, said echo suppressor including a vacuum tube, and means con; trolled by said automatic adjusting device for automatically varying the normal grid.

potential applied to said tube.

, 6. In a signaling system, a four-wire transmission circuit, an amplifier in each line of the four-wire circuit, a pilot circuit subjected to the same transmission conditions as'the lines of the four-wire circuit,

an automatic adjusting device associated with said pilot circuit, means controlled by said automatic adjustin device for adjusting the gain of said amp ifiers, an echo su pressor unit associated with each line of t e four-wire circuit, and means controlled by said automatic adjusting device for adjusting the sensitivity of said echo suppressor units to compensate for the change in' the 7. In a signaling system, a four-wire transmission circuit, an. amplifier in each line of the four-wire circuit, a pilot" circuit 'subjected to the same transmission conditions as the lines of the four-wire circuit, an automatic adjusting deviceassociated with said pilot circuit, means controlled by said automatic adjusting device 1 for adjusting the gain of said amplifiers, an echo suppressor associated with each line of the four-wire I circuit, each echo suppressor including a vacuurnjtube, and means controlled by said automatic adjusting device for varying the normal grid potential applied tol said vacuum tubes to, compensate for the change in the gain of said am lifiers. I

In testimony whereo I have signed my this 9th day'of September, 1925. Y HAROLDSHAMILTON:- 

